This invention relates to diffuser means and more particularly, in one form, to diffuser means disposed between the compressor and combustion sections of a gas turbine engine.
Typically, gas turbine engines include a compressor section which delivers pressurized air to a continuous flow combustor. The pressurized air is mixed with fuel in the combustor, burned and gaseous products of combustion are then exhausted from the combustor to a turbine which extracts energy from the gases. This invention is most applicable to gas turbine engines wherein an annular combustor is comprised of inner and outer combustor liners, defining a combustion chamber or flow path therebetween, and inner and outer walls spaced from the inner and outer liners respectively. Each of the walls define, with its respective liner, a flow path adjacent the combustion flow path. These three flow paths are annular and generally concentric with one another. Pressurized air discharged from the compressor is directed through a divergent, annular passageway commonly known as a diffuser. From the diffuser, the air stream is divided and directed into the aforementioned flow paths. Combustion is maintained in the central flow path between the combustor liners, while the outer flow paths provide air for cooling the combustor liners and additional or dilution air for enhancing combustion within the combustion flow path.
The aforementioned diffuser is provided for purposes of converting the dynamic head of pressurized fluid, in the form of air, exiting the compressor into static pressure. Ideally, it is desirable to convert the dynamic head into static pressure without any loss in total pressure. However, the efficiency or effectiveness of diffusers known in the art is less than satisfactory. Diffusers have been generally classified in two basic categories: step diffusers and controlled diffusers. Typical prior art step diffusers have a gradual expansion portion, during which approximately 60% of the dynamic head is converted into static pressure, and a sudden dump portion, during which only 25% of the remaining dynamic head is recovered. In present day gas turbine engines, where the dynamic head exiting the compressor amounts to 6% of the total pressure, the gradual expansion portion of the step diffuser would recover approximately 3.6% of the dynamic head while the dump portion of the diffuser would recover approximately 0.40% of the dynamic head. Hence, approximately 2.0% of total pressure would be lost. However, in present day engines this degree of loss of total pressure has more or less been found to be satisfactory.
In some of the next generation of advanced gas turbine engines, the dynamic head of pressurized air exiting the compressor is considerably greater than the dynamic head associated with present day engine. In some advanced engines, the dynamic head can approximate 12% to 18% of the total pressure. Fixed geometry non-bleed systems typically maintain a constant .DELTA.P/Q thus resulting in a loss of between 4.0% and 6.0% in total pressure. With conventional step diffusers, the loss of total pressure in advanced engines, then, may be approximately 2 to 3 times as great as the loss in total pressure associated with present day engines. Hence, prior art step diffusers will not meet the needs of next generation gas turbine engines.
Prior art controlled diffusing techniques are not sufficient in meeting the requirements of next generation gas turbine engines, having high dynamic fluid pressure heads at the compressor outlet, principally because of the formation of a boundary layer at the walls of the diffuser. Since the degree of divergence of the walls is relatively fixed to avoid fluid separation, the larger dynamic head requires a greater diffuser length resulting in an increase in the thickness of the boundary layer along the wall as the fluid flows through the additional length of the diffuser. Increasing boundary layer thickness reduces the efficiency of the diffuser. The present invention is addressed toward these difficulties associated with boundary layer losses found in conventional diffusers. The present invention also address the problem associated with turning the stream of pressurized fluid from the diffuser into the aforementioned concentric flow paths.
Therefore, it is an object of the present invention to provide a diffuser for use in a gas turbine engine.
It is another object of the present invention to provide a diffuser offering increased efficiency or effectiveness over diffusers heretofore known in the art.
It is yet another object of the present invention to provide a diffuser well adapted to cooperate with advanced compressors to efficiently convert the dynamic head of fluid received from the compressor into static pressure.
It is still another object of the present invention to provide means for turning the stream of fluid from the diffuser into concentric flow paths associated with the combustor of a gas turbine engine.